Test: Rankine's Theory of Bearing Capacity - Civil Engineering (CE) MCQ

σ̅ represents the effective surcharge at the base level of the foundation, assuming total unit weight for the portion of the soil above the water table and submerged unit weight for the portion below the water table.

Rankine considered the equilibrium of the other soil element (element 2) beyond the edge of the footing, but adjacent to element 1.

According to Rankine’s equation bearing capacity of cohesion less soil is zero at the ground surface.

Sometimes, the safe bearing capacity is also referred to as the ultimate bearing capacity qf divided by a factor of safety F.

The ultimate bearing capacity qf and the net ultimate capacity are connected by the following relation:
qf = qnf + σ̅ (or) qf = qf – σ̅
where σ̅ is the effective surcharge at the base level of the foundation.

The gross pressure intensity q is the total pressure at the base of the footing due to the weight of the superstructure.

The net safe bearing capacity is the net ultimate bearing capacity divided by a factor of safety F i.e., qns = qnf/F.

Rankine considered the equilibrium of two soil elements, The first one immediately below the foundation (element 1).

When the load on footing increases, and approaches a value qf, a state of plastic equilibrium is reached under the footing.

During the state of shear failure (plastic equilibrium), the following principal stress relationship exists σ1 = σ3 tan2 α + 2c tan α
for cohesion-less soil,σ1 = σ3 tan2 α.